From one aspect, the present invention relates to injection moulding apparatus. As used herein, the term injection moulding apparatus embraces apparatus used for injecting a plastics moulding composition into a mould cavity and apparatus used for injecting molten metal into a mould cavity, commonly called die-casting apparatus.
Apparatus which is commonly used for injection moulding comprises two platens, on which are fixed respective tools of a set of moulding tools. The apparatus also includes means for moving one of the platens relative to the other for opening and closing the set of tools. Means is provided for injecting a moulding composition through the tool on the stationary platen to the mould cavity, when the tools are closed. It is necessary to maintain the set of tools in a closed condition until the moulding has cooled sufficiently to acquire dimensional stability. A substantial proportion of the operating cycle of the apparatus is represented by a cooling time, during which the platens must be held stationary relative to each other. This is achieved by maintaining in operation throughout the cooling time hydraulic pumps used to establish the mould-closing pressure. One object of the present invention is to improve the efficiency of an injection moulding operation. Further objects include improving the efficiency of cooling of a set of mould tools.
According to a first aspect of the present invention, there is provided injection moulding apparatus comprising a plurality of mould sets, an injection head, transport means for imparting relative movement to the mould sets and the injection head to bring the injection head into proximity with the mould sets in sequence, feed means for feeding a moulding composition through the injection head into a mould set when that mould set is in proximity with the injection head and clamping means for clamping in a closed condition at least one of said mould sets whilst the moulding composition is injected through the injection head into the mould set.
In in accordance with the first aspect of the invention, after injection of the moulding composition into a first mould set, the injection head can be used to inject moulding composition into a second mould set before the moulding formed in the first mould sets has cooled sufficiently to permit removal of that moulding from the first mould set. The interval between successive injection operations does not depend upon the required cooling time.
According to a second aspect of the invention, there is provided a method of moulding a composition wherein an injection head is used to inject the moulding composition into each of a plurality of mould sets in turn.
According to a third aspect of the invention, there is provided an injection moulding tool set comprising first and second tool parts which collectively define a mould cavity and comprising retaining means for releasably retaining the tool parts in a closed condition. A tool set embodying the third aspect of the invention is especially suitable for use in a method according to the second aspect of the invention.
Relative movement of the mould sets and the injection head may be achieved by maintaining the injection head at an injection station and moving the mould sets in turn into the injection station. Alternatively, the relative movement may be achieved by maintaining the mould sets in respective stations and moving the injection head to those stations in turn.
The transport means used for imparting relative movement to the mould sets and the injection head may be adapted to locate each mould set in turn accurately in relation to the injection head. Alternatively, there may be provided, in addition to the transport means, locating means for locating each mould set in turn accurately relative to the injection head. The transport means may comprise a conveyor of generally known form for conveying the tool sets sequentially to the injection station. Alternatively, the transport means may comprise a track defining a path along which the mould sets move to the injection station and propulsion means for imparting motion to the mould sets which are on or in the track. The propulsion means may be adapted to drive the mould sets by means of air pressure, magnetic field or other known means. The mould sets may be guided along the track and/or supported in the path, at least when moving, by air pressure, magnetic field or other known means. In a case where the mould sets remain in respective stations and the injection head is moved from one mould set to another, the injection head may be transported by a conveyor of known kind or may be driven along a track by known propulsion means hereinbefore mentioned and supported by known means mentioned herein. Also in a case where the injection head is moved from one mould set to another, transport means for transporting the injection head may be adapted to establish accurately a predetermined position of the injection head relative to each mould set in turn or there may be provided in addition to the transport means locating means for establishing accurately the required position.
In a case where either the mould sets or the injection head are or is moved along a track, guidance along the track may be achieved by known means which do not rely upon physical contact, for example guidance by means of electromagnetic radiation or by means of an electromagnetic field associated with a conductor buried in a floor.
Means for performing operations additional to injection may be positioned at stations additional to an injection station or may be transported along the path along which the injection head is transported.
Means for applying heat to or extracting heat from the mould sets may be moved to the mould sets in turn, either following a path which is followed by the injection head or following a different path. Means for opening the mould sets may be moved to each of the mould sets in turn, either following the path along which the injection head moves or following a different path.
In a case where the mould sets are moved in turn into an injection station, the mould sets are preferably moved through additional stations including a heat transfer station and an opening station.
There may be provided a plurality of injection heads through which respective moulding compositions are injected into the mould sets. These compositions may differ in respect of colour or in respect of other characteristics. In a case where respective moulding compositions are injected through a plurality of heads into each mould set, these may be injected into each mould set concurrently through respective inlet nozzles or sequentially. An injecting relation may be established between the mould set and the injection heads in turn.
In a case where more than one injection head is provided, these may be moved along a common path from one mould set to another or may be disposed at respective injection stations through which the mould sets are transported.
In a case where means additional to one injection head moves from one mould set to another, movement of the additional means may be independent of movement of the injection head. Alternatively, these may be mounted on a common carrier which carries them to the mould sets in turn. In a case where the mould sets are mounted on a common carrier and are moved through successive stations, a particular mould set may pass through one or more stations without any operation being performed on that particular mould set at that particular station or stations. Thus, the actions to which one mould set is subjected at successive stations may be selected independently of the actions to which another mould set is subjected during travel along the same path.
According to a further aspect of the invention, injection moulding apparatus comprises a carrier for carrying a plurality of mould sets, an injection head, feed means for feeding a moulding composition through the injection head into a mould set and clamping means for clamping at least one of the mould sets in a closed condition whilst the moulding composition is injected through the injection head into that mould set, wherein the carrier is arranged for moving the mould sets, when carried on the carrier, around an orbital path, wherein the feed means is on the inside of said path and wherein the injection head extends from the feed means to said path. This arrangement has the advantage that a relatively compact apparatus can be achieved. Furthermore, there is at the outside of the orbital path space for accommodating the clamping means and this space is not restricted by the feed means and injection head.
The feed means preferably includes a feed screw which is rotatable about an axis transverse to said path. Generally, the path along which the mould sets are moved by the carrier will be horizontal. In this case, the injection head is preferably disposed at a level above the feed screw and the feed screw is arranged to feed the moulding composition upwardly to the injection head. This arrangement has the advantage that gravity will tend to cause the moulding composition to move in a direction from the injection head towards the feed screw and the risk of moulding composition escaping from the injection head under the action of gravity in an uncontrolled manner is substantially eliminated. Furthermore, the arrangement provides the possibility of removing the injection head and replacing it with a fresh injection head whilst the moulding composition is supported by the feed screw and in a molten condition.
Preferably, the moulding composition is moved upwards during melting and is injected downwards.
The apparatus preferably includes a housing which substantially encloses the moving parts of the apparatus. The atmosphere within the housing may be monitored and/or may be controlled. There may be provided inside the housing a smoke-detector or a temperature-responsive device suitable for providing an alarm signal if a fire occurs inside the housing. In the event of a fire occurring inside the housing, the housing will restrict access of air to the fire and an inert gas or other fire-extinguishing medium may be discharged inside the housing to extinguish the fire.
Operation of the apparatus is preferably controlled by a microprocessor. Information relating to mouldings to be produced by the apparatus and relating to mould sets present in the apparatus may be applied to the microprocessor through known input devices, for example a keyboard, a disc drive or a tape reader. The microprocessor may have an interface with other components of a control system of the apparatus which facilitates the transfer of information between the control system of one apparatus embodying the invention and the control system of further apparatus. Thus, if a programme suitable for controlling operation of the apparatus to produce certain mouldings is applied to the microprocessor of first apparatus, that programme may be transferred to further apparatus or the further apparatus may be controlled by the microprocessor of the first apparatus to cause the further apparatus to produce the same or similar mouldings.
The clamping means may remain at the injection station in a case where the mould sets are moved through the injection station. Alternatively, the clamping means may move with the mould sets through the injection station and other stations. In a case where the injection head moves to the mould sets in turn, the clamping means also may be moved to each of the mould sets in turn. Alternatively, respective clamping means may be provided for each mould set, the clamping means remaining with the mould set when the injection head moves from one mould set to another.
Preferred features of injection moulding apparatus in accordance with the first aspect of the invention and other aspects of the invention are defined in the claims appended hereto.